None.
Not Applicable.
The present invention relates generally to load cells of the type used to measure forces and moments, and more particularly, to a ring load cell configured for placement around an axially disposed shaft to provide thermally compensated force and moment measurements in an orthogonal three-axis coordinate system.
It is frequently necessary to measure applied forces and moments between a motor or gear drive and a shaft driven component. Usually, the forces and moments acting upon such a mechanical system are expressed in terms of a three-dimensional coordinate system, and may be completely expressed in terms of six components, including three linear force components along each of three mutually orthogonal axes and three moments about the same set of axes.
A conventional approach to developing force sensors for measuring these six components is to use mechanical structures including various hinges, pivots, or other mechanisms to decouple the force components and to permit them to be measured independently from one another. Such mechanical structures are complex to manufacture, and require precise accuracy in dimensions and component elasticities to accurately decouple the individual force components. Accordingly, such structures are costly to manufacture and maintain.
An alternative approach which has been developed to overcome some of the problems associated with mechanically decoupling the various forces and moments to be measured is to use strain-based force sensors as is exemplified by U.S. Pat. No. 4,094,192 to Watson, et al. The system disclosed in the U.S. Pat. No. 4,094,192 patent employs shear strain gages and extensional gages mounted on beams disposed between a pair of annular rings to measure forces and moments acting on the ring. Signals from the individual sensors are processed by an analog or digital processor to derive the desired force and moment components in an orthogonal three-axis coordinate system without the need to know the dimensions or elasticities of the structure upon which the sensors are mounted. However, the design shown in the U.S. Pat. No. 4,094,192 patent results in a trade off of gage sensitivity between the shear strain gages and the extensional gages, which are mounted to the same beams.
There is an ongoing need to provide an improved compact multi-axis load cell particularly suited for use about a shaft disposed between a driving component and a driven component, and which can be selectively configured for sensitivity to forces or moments depending upon the particular application in which it is employed.
Briefly stated, the present invention is a ring load cell configured to measure three force components and three moment components in an orthogonal three-axis coordinate system, together with one or more temperature components. The ring-load-cell structure consists of two annular flanges having a common central axis through which a shaft may be disposed. The annular flanges are interconnected by a plurality of filleted posts configured to enhance strain distribution and which are disposed parallel to the common central axis, equally spaced about the circumference of the annular flanges. A plurality of strain gauges is disposed either on the posts or on the fillets, and a plurality of temperature sensors are disposed either on the posts or on the inner surfaces of the annular flanges. Signals from the strain gauges and temperature sensors are processed to provide thermally compensated strain measurements of the applied forces and moments on the ring-load-cell structure in the orthogonal three-axis coordinate system.
The foregoing and other objects, features, and advantages of the invention as well as presently preferred embodiments thereof will become more apparent from the reading of the following description in connection with the accompanying drawings.